1. Field of the Invention
The present invention relates to a gas discharge tube; and, in particular, to a gas discharge tube for use as a light source for a spectroscope, chromatography, or the like.
2. Related Background Art
As techniques in such a field, those disclosed in Japanese Patent Application Laid-Open Nos. HEI 7-326324, HEI 8-77979, and HEI 8-222185 have conventionally been known. In the gas discharge tubes described in these publications, a sealed envelope is constituted by a side tube made of glass and a stem made of glass. Plugged into the stem are stem pins securing anode and cathode sections, respectively. The sealed envelope is filled with about several Torr of deuterium gas, for example. Such a gas discharge tube is called deuterium lamp and is utilized as a stable UV light source.
In order to carry out point emission, such a deuterium lamp is configured such that a focusing electrode plate having a small hole at its center is positioned at the front face of the anode section, i.e., on the cathode section side, so as to converge the thermions generated in the cathode section. The distance between the focusing electrode plate and the anode section is the most influential parameter for point emission characteristics, and various techniques have been developed for improving and maintaining its accuracy.
Though the techniques developed so far can achieve the accuracy, it requires a skill for processing and assembling, and materials themselves become expensive, whereby it has been problematic in the easiness and stability of processing/assembling, in terms of cost, and so forth.
In view of these problems, it is an object of the gas discharge tube in accordance with the present invention to provide a gas discharge tube which is easy to process/assemble, can be made stably, and can cut down the cost.
For overcoming the above-mentioned problems, the gas discharge tube in accordance with the present invention is a gas discharge tube having a sealed envelope at least a part of which transmits light, the sealed envelope being filled with a gas and being provided with anode and cathode sections disposed therein, electric discharge being generated between the anode and cathode sections, so that the light-transmitting part of the sealed envelope emits predetermined light outside. The gas discharge tube comprises an insulating anode support member mounting the anode section, an insulating focusing electrode support member, mounted on a surface of the anode support member surrounding the anode section, having an opening on the anode section, and a focusing electrode, securely disposed at a front face of the opening of the focusing electrode support member, having a focusing opening projecting toward the anode section. The cathode section is disposed on the anode support member or focusing electrode support member so as to be spaced from the focusing opening.
As a consequence of such a configuration, when the anode section and the focusing electrode support member are mounted on the anode support member, and the focusing electrode is disposed at the front face of the focusing electrode support member, whereas the cathode section is spaced from the focusing electrode, then the respective electrodes can be assembled with a highly accurate positional relationship in a simple operation. While the accuracy in their positional relationship depends on the precision of the anode support member and focusing electrode support member, the respective support members are separated from each other, whereby the precision in the securing portion of each electrode can easily be enhanced, and the manufacturing cost can be cut down.
Preferably, the anode support member has a cavity portion for mounting the anode section. As a consequence, it becomes quite easy to secure the anode section.
The anode section may be secured by being held between the anode support member and the focusing electrode support member. As a consequence, not only the accuracy in securing the anode section but also the accuracy in distance between the anode section and focusing electrode can further be improved.
Preferably, the anode support member and focusing electrode support member are made of ceramics. This makes it easier to improve the processing and precision, and can cut down the manufacturing cost as well.
Preferably, the anode support member or focusing electrode support member have pin holes through which stem pins securing the anode section, cathode section, and focusing electrode to the sealed envelope, respectively, penetrate. As a consequence, each electrode can be secured more reliably, and the accuracy in positional relationship improves.
Preferably, the anode support member is disposed in contact with a stem forming a bottom face of the sealed envelope. As a consequence, the heat generated in the anode and focusing electrode are rapidly transmitted to the stem by way of the focusing electrode support member and the anode support member, whereby fluctuations in the mutual positional relationship between the anode and focusing electrode which may occur due to their thermal deformations can be prevented from occurring.